Čoh, M. et al.: KINEMATICS OF ’S MAXIMAL VELOCITY Kinesiology 50(2018)2:172-180

KINEMATICS OF USAIN BOLT’S MAXIMAL SPRINT VELOCITY

Milan Čoh1, Kim Hébert-Losier2, Stanko Štuhec1, Vesna Babić3, and Matej Supej1 1University of Ljubljana Faculty of , Slovenia 2University of Waikato, Faculty of Health, Sport, and Human Performance, Adams Centre for High Performance, New Zealand 3University of Zagreb, Faculty of Kinesiology, Croatia

Original scientific paper https://doi.org/10.26582/k.50.2.10 UDC: 796.42:577

Abstract: This study investigated the maximal sprint velocity kinematics of the fastest 100 m sprinter Usain Bolt. Two high-speed video cameras recorded kinematics from 60- to 90-m marks during the men 100 m final at the IAAF World Challenge Zagreb 2011, Croatia. Despite a relatively slow reaction time (194 ms), Bolt won in 9.85 s (mean velocity: 10.15 m/s). His fastest 20-m section velocity was 12.14 m/s, reached between 70- and 90-m marks, by 2.70 m long strides and 4.36 strides/s frequency. At the maximal velocity, his contact and flight times were 86 and 145 ms, respectively, and vertical ground reaction force generated equalled 4.2 times his body weight (3932 N). The braking and propulsion phase represented 37% and 63% of ground contact, respectively, with his centre of mass (CoM) exhibiting minor reductions in horizontal velocity (2.7%) and minimal vertical displacement (4.9 cm) emerged Bolt’s maximal sprint velocity and international predominance from his coordinated motor abilities, power generation capacities, and effective technique. This study confirms that his maximal velocity was achieved by means of relatively long strides, minimal braking phase, high vertical ground reaction force, and minimal vertical displacement of CoM. This study is the first in-depth biomechanical analysis of Bolt’s maximal sprinting velocity with the segmental reconstruction.

Key words: 100 m sprint, athletics, biomechanics, sport performance, sprint

Introduction literature has attempted to explain Bolt’s perfor- Usain Bolt is one of the greatest athletes in mance using spatio-temporal parameters (Graubner the history of athletics. He is the winner of eight & Nixdorf, 2011; Maćkała & Mero, 2013), math- Olympic gold medals, as well as the world record ematical and biomechanical models (Beneke & holder in the 100 m (9.58 s), 200 m (19.19 s), and 4 x Taylor, 2010; Eriksen, Kristiansen, Langangen, & 100 m relay (36.84 s). During the 12th International Wehus, 2009; Graubner & Nixdorf, 2011; Taylor & Association of Athletics Federations (IAAF) World Beneke, 2012), as well as anthropometrical charac- Championships in in 2009, he established a teristics (Charles & Bejan, 2009; Maćkała & Mero, new 100 m world record with a tailwind of 0.9 m/s, 2013). There has also been attempts to estimate beating his previous world record by 0.11 s that Bolt’s 100 m sprinting potential (Barrow, 2012; had been set in 2008. Specifically, his 100 m world Eriksen, et al., 2009), with a general consensus that record was one of the most remarkable achieve- he could have run below 9.5 s if only his reaction ments in sprinting and was the largest improvement time had been better and under optimal environ- in the 100 m world record yet observed (Graubner mental conditions (i.e., tailwind and high altitude), & Nixdorf, 2011). Recently, at the 15th IAAF World thus agreeing with the prediction by Denny (2008) Championships in , 2015, Bolt managed to that humans can run 100 m in 9.48 s. However, kine- maintain his world titles in the 100 m, 200 m, and matic data of Bolt running in competition are rare, 4 x 100 m relay despite participating in few compe- and a more detailed investigation for Bolt’s whole- titions prior to the Championships due to injury. body kinematics could assist in verifying some of Bolt’s performance has been a subject of the numerous theories of his sprinting success. numerous media analyses, debates, and discussions, When Bolt set his current 9.58 s world record, as well as biomechanical investigations. Research his fastest 20-m section time was 1.61 s, reflecting

172 Čoh, M. et al.: KINEMATICS OF USAIN BOLT’S MAXIMAL SPRINT VELOCITY Kinesiology 50(2018)2:172-180 a mean velocity of 12.42 m/s (Graubner & Nixdorf, In a first instance, the videos from the 2011)1. This value is the highest absolute velocity broadcasters were used in conjunction with those ever reached by a sprinter during a 100 m race, from our cameras and the official race results to and the fastest mean velocity (10.60 m/s) over that count the total number of strides taken and to race distance. Bolt’s superior sprinting performance compute the mean velocity, stride length, and has been attributed to a strong acceleration phase, stride frequency of each competitor. Bolt’s data higher maximal velocity, advantageous power were compared to his fellow competitors and to his generation ability, and impressively long strides data available from previous races (Arribas, 2012; associated with his physical built (Beneke & Taylor, Hommel, 2009; Maćkała & Mero, 2013). Secondly, 2010; Graubner & Nixdorf, 2011). the instance of Bolt’s maximal sprint velocity Bolt participated in the IAAF World Challenge reached was isolated (~85 m) and relevant kine- Zagreb 2011, Croatia. Our team of scientists had matic parameters were extracted over the fastest the opportunity to further study the fastest sprinter 20-m section of his (70 to 90 m). For data extrac- in the world. The specific aim was to investigate tion, the computer program APAS (Ariel Perfor- the kinematic parameters associated with Bolt’s mance Analysis System, Ariel Dynamics Inc., Coto maximal sprint velocity during the men 100 m de Caza Trabuco Canyon, USA) was used to recon- finals. struct a 2D full-body biomechanical model using 16 reference points (Winter, 2005), which included the Material and methods metatarsals; the ankle, knee, hip, shoulder, elbow, and wrist joints; and two head markers. The coor- The IAAF World Challenge in Zagreb, Croatia, th dinate data from these 16 points were smoothed was held on September 13 , 2011, at the Sports Park using a low-pass second-order Butterworth digital Mladost. Prior to this observational research project filter with a 14 Hz cut-off frequency and used to with a case study design, permission to record video define 15 segments and the centre of mass (CoM) footage of the men 100 m sprint final was granted by of the model according to standard anthropometric the Technical Delegate and Organizing Committee tables (Winter, 2005). Although the 300-Hz data of the European Athletics Association. The temper- capturing frequency was used to determine flight o ature on the day of the competition reached 23 C, and contact times, video digitization was performed and there was a head wind of 0.1 m/s during the at 100 Hz to reduce redundancy and manual labour. event (IAAF, 2011). The primary athlete of interest The joint position accuracy was estimated to < 2 cm was Usain Bolt (age: 25 years, height: 1.96 m, in the sagittal plane based on the resolution of the weight: 86 kg; country: ). The other final- system, measurement area, and typical manual digi- ists were (35 years, and tization error. Nevis), Richard Thompson (26 years, Trinidad and The running stride (distance from foot strike to Tobago), Jaysuma Saidy Ndure (27 years, ), foot strike of the same foot) was divided into the Mario Forsythe (25 years, Jamaica), ground contact (time of foot strike to toe off) and (29 years, the ), and flight (time of toe off to foot strike) phases for both (26 years, the United States). the left and right leg. The ground contact phase To record kinematic data from Bolt running, was further divided into the braking and propulsion two high-speed digital cameras (EX-F1, Casio phases according to the horizontal position of the Computer Co., Ltd., Tokyo, Japan), sampling at 300 CoM in reference to the ankle (braking: the CoM Hz with a pixel resolution of 720 x 576, were strate- is in front of the ankle joint; propulsion: the CoM gically placed along the track to capture data from is behind the ankle joint), and included an instance the 100 m sprint. Prior to the race start, two refer- of maximal amortization coinciding with the ence frames (dimension: 2 m x 2 m x 2 m) were used maximal knee flexion. From the digitized videos, to calibrate the final section (60 to 90 m) of Bolt’s the following kinematic parameters were extracted lane. The calibration procedure considered eight to describe Bolt’s mechanics during his fastest 20-m points from the two reference frames. Furthermore, section: stride length; stride frequency; ground to accurately quantify the sprinting dynamics of all contact time; flight time; braking time; propulsion seven competitors, an additional high-speed camera time; CoM height; CoM’s horizontal and vertical was placed closer to the start of the race and video velocities during braking, propulsion, and maximal footage from the six official sports broadcasters amortization; horizontal displacement of the CoM televising the event were acquired. The official during ground contact; distance between the foot reaction and finishing times of all sprinters were and the vertical projection of the CoM at the ground acquired from the IAAF results of the IAAF World contact; foot-CoM angle (angle formed using a line Challenge Zagreb 2011. connecting the CoM to the metatarsal relative to the

1 In the same biomechanical analysis of the 12th IAAF World Championships, Bolt’s maximal velocity was reported to be 12.34 m/s, reached at the 67.90-m mark of the race.

173 Čoh, M. et al.: KINEMATICS OF USAIN BOLT’S MAXIMAL SPRINT VELOCITY Kinesiology 50(2018)2:172-180 ground) at the foot strike and toe off; foot-ground won the race in 9.85 s, which was 0.16 s ahead of angle (angle formed using a line connecting the his closest competitor. Bolt had the least number metatarsal to the ankle joint relative to the ground) of strides, slowest stride rate, and longest strides, at the foot strike and toe off; knee angle and angular which were equal to 1.25 times his body height. velocity; foot horizontal velocity; and thigh angular velocity. Left- and right-leg values were extracted Bolt versus himself and side-to-side differences were investigated for Bolt’s 100 m sprint time at the World Challenge key parameters. In addition, the maximal vertical in Zagreb was 0.27, 0.22, and 0.16 s slower than force (F ) was calculated according to a sine-wave max his times at the 2009 Berlin World Championships, model (Taylor & Beneke, 2012) using the following 2012 Olympics, and 2008 Beijing Olym- equation: pics, respectively (Table 2). In Zagreb, his reac- π tf Fmax = mg * * ( + 1) (1) tion time, stride rate, and fastest 20-m section were 2 tc slower than those recorded in Beijing, Berlin, and where m was Bolt’s body mass (kg), g the gravita- London. His fastest 20-m section in Zagreb was tional acceleration (9.81 m/s), tf was the flight time also reached later in the race (70 to 90 versus 60 (s) and tc the ground contact time (s). to 80 m). In contrast, when setting his 9.58 s world record in Berlin, Bolt posted his quickest reaction Results time, took the least number of strides, and ran his fastest 20-m section in comparison to the other Bolt versus his competitors three events herein presented. In Berlin, he reached The race results and stride parameters of all the his maximal velocity ~20 m earlier than in Zagreb, 100 m finalists are presented in Table 1. Despite reaching 99% of his maximal velocity at 48.18 m having the slowest reaction time (194 ms), Bolt and his maximal velocity at 65 m (Hommel, 2009).

Table 1. Summary of race results and stride parameters of all the sprinters (n = 7) competing in the men 100 m finals at the IAAF World Challenge Zagreb 2011

Stride Reaction Velocitya Stride count Stride Athlete Race time (s) frequencya time (ms) (m/s) (n) lengtha (m) (Hz)

Usain Bolt 9.85 194 10.15 41.00 4.16 2.44 Kim Collins 10.01 181 9.99 49.25 4.92 2.03 Richard Thompson 10.03 177 9.97 44.50 4.44 2.25 Jaysuma Saidy Ndure 10.13 167 9.87 43.25 4.27 2.31 Mario Forsythe 10.16 188 9.84 46.50 4.58 2.15 Justin Gatlin 10.17 177 9.83 43.25 4.25 2.31 Ivory Williams 10.37 156 9.64 49.00 4.73 2.04

Note: a Values are means over the 100 m race.

Table 2. Summary of Usain Bolt’s race results, stride parameters, and fastest 20-m sections during the men 100 m finals at the 2008 Beijing , 2009 Berlin World Championships, IAAF World Challenge Zagreb 2011, and 2012 London Olympic Games

Fastest Stride Stride Fastest Race Race time Reaction Velocitya Stride 20-m frequencya lengtha 20-m (year) (s) time (ms) (m/s) count (n) velocityb (Hz) (m) section (m/s)

Beijing OG 9.69 166 10.32 41.10 4.24 2.43 12.20 60–80 (2008)c,d Berlin WC (2009)e 9.58 146 10.44 40.92 4.27 2.44 12.42 60–80 IAAF WoC 9.85 194 10.15 41.00 4.16 2.44 12.14 70–90 (2011) c,d London OG 9.63 165 10.38 41.40 4.30 2.42 12.35 60–80 (2012)c,d

Note. a Values are means over the 100 m race. b Values are means over the fastest 20-m section. Source: cMaćkała and Mero2; dArribas10; eHommel11. Abbreviations: OG – Olympic Games; WC – World Championships; IAAF WoC – IAAF World Challenge Zagreb 2011.

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Bolt’s fastest 20-m section contact, the angle between the longitudinal axis Stride and kinematic parameters relating of Bolt’s foot and the ground was 19.5°, indica- to Bolt’s fastest 20-m section (70 to 90 m) are tive of a plantar-flexed position. At the beginning presented in Table 3. His fastest strides were, on of ground contact, the horizontal velocity of the average, 11% quicker and 5% longer than their CoM was 11.44 m/s. This velocity decreased to corresponding means shown in Table 2, reaching 11.13 m/s (-2.8% from the initial contact) during 1.38 times his body height. Bolt’s right-leg stride the braking phase and reached 12.04 m/s (+8.2% was 2.8% quicker and 1.5% shorter than his left- from braking) by the end of the propulsion phase. leg stride and was associated with a 10 ms (6.7%) The lowest vertical CoM position occurred at the shorter flight time, 5 ms (6.0%) longer contact time, instance of maximal amortization (a maximal knee 1.4 cm (34.1%) larger vertical displacement of the flexion), where the knee was bent to ~145°. The CoM, and 287 N (7.7%) smaller maximal Fmax. range of vertical displacement of the CoM during Bolt’s whole-body dynamics during his fastest Bolt’s fastest stride was 4.9 cm, the equivalent of 20-m section at the IAAF World Challenge Zagreb 2.5% of his body height. 2011 are illustrated in Figure 1, with key results Graphical representations of linear velocities of summarized here. In the illustrated stride, the the feet and angular velocities of the knees during distance between the foot and the vertical projec- Bolt’s fastest 20-m section are provided in Figures tion of the CoM at foot strike was relatively small 2 and 3, respectively. During the ground contact (34 cm or 17.4% of his body height). At the ground phase, the mean horizontal velocity of the swinging

Table 3. Stride and kinematic parameters during Usain Bolt’s fastest 20-m section of the 100 m finals at the IAAF World Challenge Zagreb 2011

CoM vertical Stride rate Stride Flight time Contact Braking Propulsion Stride displacement F (N) (Hz) length (m) (ms) time (ms) phase (%) phase (%) max (cm)

Right 4.42 2.68 140 88 35 65 5.5 3434 Left 4.30 2.72 150 83 40 60 4.1 3720 Meana 4.36 2.70 145 86 37 63 4.5 3560

a Note. Values are means for the right and left strides. Abbreviations: CoM – centre of mass; Fmax – maximal vertical force.

Figure 1. Representation of the whole-body dynamics during Usain Bolt’s fastest 20-m section of the 100 m finals at the IAAF World Challenge Zagreb 2011.

175 Čoh, M. et al.: KINEMATICS OF USAIN BOLT’S MAXIMAL SPRINT VELOCITY Kinesiology 50(2018)2:172-180 leg foot was 16.76 m/s during braking and 23.42 high angular velocities at the knee of the swinging m/s during propulsion. The horizontal velocity of leg were observed, reaching ~850o/s towards the the swinging leg foot reached nearly twice that of end of the contact phase (Figure 3). the horizontal velocity of the CoM. Concurrently,

Figure 2. The linear velocities of the right (RF) and left (LF) feet during Usain Bolt’s fastest 20-m section of the 100 m finals at the IAAF World Challenge Zagreb 2011. The thicker bolded line separates the contact and flight phases, and the thinner bolded line separates the braking and propulsion phases.

Figure 3. The angular displacements (where 180° represents knee in full extension) and velocities (where positive values represent knee extension) of the right (RK) and left (LK) knees during Usain Bolt’s fastest 20-m section of the 100 m finals at the IAAF World Challenge Zagreb 2011. The thicker bolded line separates the contact and flight phases, and the thinner bolded line separates the braking and propulsion phase.

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Discussion and conclusion elite sprinters (Čoh, Milanović, & Kampmiller, At the IAAF World Challenge Zagreb 2011, 2001; Donati, 1995; Lehmann & Voss, 1997; Mero here investigated, Bolt won the 100 m finals in 9.85 s & Komi, 1986), Bolt’s physique obviously confers despite a rather slow reaction time. Compared to him a stride-length advantage in outperforming his competitors, Bolt took fewer and less frequent his competitors. When Bolt set the world record strides. However, these strides were on average 12% in the 100 m sprint, his mean stride frequency and longer, which was a deterministic factor in his 1st stride length were 4.27 Hz and 2.44 m, respectively place finish. His fastest 20-m section was run in (Hommel, 2009), whereas the corresponding mean 12.14 m/s between 70 m to 90 m, which was reached values of the other seven finalists were 4.51 Hz and later in the race than his usual fastest 20-m section, 2.23 m, respectively. Bolt became the first athlete in probably due to a slower start and initial accelera- the history of athletics to sprint 100 m in less than 41 tion phase. strides. Again, Bolt’s superior stride length distin- Despite being 0.27 s slower compared to his guished him from his competitors. Throughout world record, Bolt’s performance in IAAF World history, the 100 m sprint world record holders Challenge Zagreb 2011 was nonetheless remarkable have become taller, heavier and leaner (Charles & and would have won the gold medal for him that Bejan, 2009). Together with Bolt’s stature (body year at the World Championships where he height = 1.95 m) and remarkable outcomes, these was disqualified due to a . Scrutinizing data are challenging the common belief that taller his race performance using high-speed cameras individuals are at a disadvantage when it comes and a methodological approach is worthwhile in to sprinting. The current study confirms that his comprehending his unparalleled sprint achieve- maximal sprint velocity is achieved by relatively ments. During his fastest 20-m section in the long strides rather than a high stride frequency, as analysed race, Bolt’s mean flight and contact times well as by the minimal braking phase, high vertical were 145 and 86 ms, respectively, with the braking ground reaction forces, and low vertical displace- and propulsion phases representing 37% and 63% ment of the CoM. of the ground contact. Kinetically, he developed a Contact time is the key parameter differenti- maximal vertical ground reaction force equal to 4.2 ating between elite sprinters (Čoh, et al., 2001). In times his body weight (3560 N) and exhibited minor the world-class athletes’ sprinting, contact time changes in the horizontal velocity (0.31 m/s, 2.7%) is extremely short and lasts between 70 to 95 ms and vertical position (4.9 cm, 2.5% body height) of (Mann & Sprague, 1980; Mero, et al., 1992; Taylor his CoM, suggestive of an effective sprint running & Beneke, 2012), during which time sprinters technique where displacement is oriented horizon- must develop high mass-specific ground reac- tally rather than vertically. tion forces reported to range from ~1.8 to 4 times Sprint velocity is a product of stride length and their body weight (Hunter, Marshall, & McNair, frequency, where an increase in running velocity 2005; Morin, Jeannin, Chevallier, & Belli, 2006; is demonstrated to result from an increase in Taylor & Beneke, 2012). In our investigation, Bolt’s both stride length and frequency up to ~90% of maximal ground reaction force reached 4.2 times maximal velocity beyond which further increments his body weight, which is clearly superior to all rely primarily on changes in frequency (Mero & his fellow sprinters and at the top end of the spec- Komi, 1986). That said, the two parameters are trum. The forces we derived from the men 100 m interdependent, with their relationship being indi- final in IAAF World Challenge Zagreb 2011 are vidual-specific (Donati, 1995) and mediated by comparable to those previously reported for Bolt several factors, including anthropometrics (Hunter, and exceeded those reported for other interna- Marshall, & McNair, 2004), sprinting mechanics tional-level sprinters (Morin, et al., 2006; Taylor (Hunter, et al., 2004; Mann & Sprague, 1980), motor & Beneke, 2012). Although the between-study abilities (Maćkała, Fostiak, & Kowalski, 2015; differences might be in part due to different meas- Mann & Sprague, 1980), and the central nervous urement methods (e.g., error associated with esti- system (Gollhofer & Kyröläinen, 1991; Mero, Komi, mating ground reaction forces from kinematics & Gregor, 1992). While stride length depends on rather than directly from force-measuring instru- body height, leg length, and the ability of the leg ments), the data nonetheless illustrate Bolt’s ability extensors to generate high ground reaction forces to develop high vertical ground reaction forces over (Hunter, et al., 2004; Maćkała, et al., 2015; Mero, a relatively short period of time. Beneke and Taylor et al., 1992), stride frequency further relies on the (2010) suggest that Bolt generates greater mechan- cortical and sub-cortical level of the central nervous ical power per muscle fibre than his fellow competi- system (Gollhofer & Kyröläinen, 1991; Hunter, tors. Our force estimates support their proposition et al., 2004). Although it has been proposed that that Bolt benefits from superior biomechanical effi- stride frequency plays a more deterministic role ciency and relative power generation compared to in the realization of maximal velocity than stride his fellow competitors. length and that the former discriminates between

177 Čoh, M. et al.: KINEMATICS OF USAIN BOLT’S MAXIMAL SPRINT VELOCITY Kinesiology 50(2018)2:172-180

Although the contact and flight times provide (19.5°, Figure 1), and is suggestive of the plantar- vital information in terms of sprinting mechanics flexors’ pre-activation prior to the ground contact. and performance, the ability to minimize the nega- A high horizontal velocity of the swinging foot tive impacts of the braking phase and maximize is important to preserve the horizontal velocity of the positive return from the propulsion phase is the CoM during sprinting (Lehmann & Voss, 1997). also noteworthy (Mero, et al., 1992). The shorter In IAAF World Challenge Zagreb 2011, 100 m race, the braking phase, the smaller the reduction in the mean horizontal velocity of Bolt’s swinging the CoM horizontal velocity (Hunter, et al., 2004; foot during the braking and propulsion phase was Mann & Sprague, 1980). At maximal velocity, the 16.76 m/s and 23.42 m/s, respectively, with the latter braking phase of elite male sprinters is reported being approximately twice the velocity of the CoM. to represent ~43% of ground contact (Mero, et al., The angular velocity of the thigh segment of the 1992). Herein, Bolt’s braking phase represented swinging leg ensures the horizontal velocity of the only 37% of his ground contact, with the remaining foot. Lehmann and Voss (1997) recorded maximal 63% being utilized for propulsion. Bolt’s horizontal angular velocities of the swinging leg from 500 to CoM velocity during braking decreased by 2.8% 800o/s in sprinters running at least 10.50 m/s and only, and subsequently increased by 8.2% during found positive correlations between the thigh’s propulsion, again supporting that Bolt is effec- angular velocity and a sprinter’s absolute velocity. tive at minimizing the impacts during braking In mid-stance, Bolt’s angular velocity of the thigh and maximizing the positive return during propul- was 587o/s, which is at the lower end of the spec- sion. Furthermore, as running velocity increases trum reported by Lehmann and Voss most likely and contact time decreases, there is a reduction in due to his anthropometric characteristics, longer the vertical displacement of the CoM in response body segments, and slower stride frequency. to a need to increase horizontal force production Compared to his 100 m sprint performances (Brughelli, Cronin, & Chaouachi, 2011). Bolt exhib- at the 2008 Beijing Olympics, 2009 Berlin World ited minor vertical CoM displacement (4.9 cm or Championships, and 2012 London Olympics, Bolt’s 2.5% of his body height) during his fastest 20-m slower time in IAAF World Challenge Zagreb 2011 section in Zagreb. In elite athletes, vertical CoM can be explained by several factors, such as the displacement during maximal sprinting is reported standard of competition (Hollings, Hopkins, & to range from 4.7 to 12 cm (Hébert-Losier, Mourot, Hume, 2012), environmental conditions (Holl- & Holmberg, 2015; Mann & Sprague, 1980; Mero, ings, et al., 2012; Linthorne, 1994), and sprinting et al., 1992). The low vertical oscillation of the CoM mechanics (Hommel, 2009). For instance, Olym- observed here in Bolt highlights his high biome- pics and World Championships produce consider- chanically efficiency and movement economy. ably faster 100 m times (~0.8%) compared to other The position of the foot in relation to the vertical competitions (Hollings, et al., 2012), all else being projection of the CoM at the foot strike influences similar. up to the allowed IAAF the braking phase (Hunter, et al., 2005), with the limit of 2 m/s for the record time recognition can general recommendation being to foot strike as improve 100 m times by ~1 ms compared to the close as possible to a point below the CoM (Brown without-wind condition (Hollings, et al., 2012; & Ferrigno). At his maximal velocity, the distance Linthorne, 1994). During his world record 100 m between Bolt’s foot and vertical projection of his performance in Berlin, Bolt’s reaction time was CoM at the ground contact was relatively small (34 quicker, stride count lower, maximal velocity faster cm or 17% of his body height), which was consistent and reached sooner in the race (Hommel, 2009), and with mechanics of sprinters running under 11 s on wind conditions were slightly more favourable than 100 m (Ito, Fukuda, & Kijima, 2008). It is also in IAAF World Challenge Zagreb 2011, which could generally recommended that sprinters strike the all contribute to explaining the 2.8% performance ground with the ankle in plantar-flexion to fully difference observed between these two races. utilize the stretch-shortening cycle potential. An During Usain Bolt’s fastest 20-m section at the effective stretch-shortening cycle of the plantar- IAAF World Challenge Zagreb 2011, 100 m finals, flexors during the ground contact phase of running his performance was associated with a relatively requires a pre-activation of the muscles (before the long stride length, horizontal positioning of the foot ground contact) prior to a rapid eccentric (stretch) close to the CoM at the ground contact, minimal phase at the ground contact immediately followed braking phase, high vertical ground reaction forces, by a concentric (shortening) phase (Komi, 2000). minimal vertical displacement of the CoM, as well Both the central and peripheral neural components as with high angular and horizontal velocities of are involved in optimizing the stretch-shortening his swinging leg. This study is the first in-depth cycle during running. In the current study, the angle biomechanical analysis with segmental reconstruc- formed by the longitudinal axis of the foot and the tion of Bolt’s maximal sprinting velocity during ground indicates plantar-flexion at the foot strike an international competition. The results from this

178 Čoh, M. et al.: KINEMATICS OF USAIN BOLT’S MAXIMAL SPRINT VELOCITY Kinesiology 50(2018)2:172-180 study can be used as a model for further devel- tion, speed-maintenance, and deceleration) can be oping specific aspects of maximal sprinting velocity suggested to fully comprehend Bolt’s performance. in elite athletes and improve our understanding of For now, Bolt’s predominance is suggested to be a Bolt’s predominance in sprinting. resulting combination of anthropometrical charac- A more extensive analysis including all the teristics, coordinated motor abilities, power gener- sprinting phases (i.e., starting block, accelera- ation capacities, and effective running technique.

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Submitted: September 6, 2017 Accepted: July 10, 2018 Published Online First: October 30, 2018

Correspondence to: Prof. Milan Čoh, Ph.D. University of Ljubljana, Faculty of Sport Gortanova 22, 1000 Ljubljana, Slovenia Phone: 041-729-356 Fax: +386 1 520 77 40 E-mail: [email protected]

Acknowledgements The authors would like to thank members of the Organizing Committee of IAAF World Challenge Zagreb 2011 for facilitating this research project. This study was supported by the Slovenian Research Agency (ARRS).

Disclosure statement The authors have no potential conflicts of interest to disclose.

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